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Subject: Re: [PATCH] um: add a generic "fd" vector transport
To:     =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= <marcandre.lureau@redhat.com>,
        linux-um@lists.infradead.org
Cc:     joerd.simons@collabora.co.uk, richard@nod.at, jdike@addtoit.com,
        linux-kernel@vger.kernel.org, alex.dewar@gmx.co.uk
References: <20200407202853.1791218-1-marcandre.lureau@redhat.com>
From:   Anton Ivanov <anton.ivanov@cambridgegreys.com>
Organization: Cambridge Greys
Message-ID: <8a6dced2-886f-f8bd-aff9-3793f418cb0e@cambridgegreys.com>
Date:   Tue, 7 Apr 2020 22:02:12 +0100
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On 07/04/2020 21:28, Marc-André Lureau wrote:
> Learn to take a pre-opened file-descriptor for vector IO.
> 
> Instead of teaching the driver to open a FD in multiple ways, it can
> rely on management layer to do it on its behalf. For example, this
> allows inheriting a preconfigured device fd or a simple socketpair()
> setup, without further arguments, privileges or system access by UML.
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>   arch/um/drivers/vector_user.c | 59 +++++++++++++++++++++++++++++++++++
>   1 file changed, 59 insertions(+)
> 
> diff --git a/arch/um/drivers/vector_user.c b/arch/um/drivers/vector_user.c
> index 29fae0456ade..45c1550dbb37 100644
> --- a/arch/um/drivers/vector_user.c
> +++ b/arch/um/drivers/vector_user.c
> @@ -29,6 +29,7 @@
>   #include <netdb.h>
>   #include <stdlib.h>
>   #include <os.h>
> +#include <limits.h>
>   #include <um_malloc.h>
>   #include "vector_user.h"
>   
> @@ -42,6 +43,9 @@
>   #define TRANS_RAW "raw"
>   #define TRANS_RAW_LEN strlen(TRANS_RAW)
>   
> +#define TRANS_FD "fd"
> +#define TRANS_FD_LEN strlen(TRANS_FD)
> +
>   #define VNET_HDR_FAIL "could not enable vnet headers on fd %d"
>   #define TUN_GET_F_FAIL "tapraw: TUNGETFEATURES failed: %s"
>   #define L2TPV3_BIND_FAIL "l2tpv3_open : could not bind socket err=%i"
> @@ -347,6 +351,59 @@ static struct vector_fds *user_init_unix_fds(struct arglist *ifspec, int id)
>   	return NULL;
>   }
>   
> +static int strtofd(const char *nptr)
> +{
> +	long fd;
> +	char *endptr;
> +
> +	if (nptr == NULL)
> +		return -1;
> +
> +	errno = 0;
> +	fd = strtol(nptr, &endptr, 10);
> +	if (nptr == endptr ||
> +		errno != 0 ||
> +		*endptr != '\0' ||
> +		fd < 0 ||
> +		fd > INT_MAX) {
> +		return -1;
> +	}
> +	return fd;
> +}
> +
> +static struct vector_fds *user_init_fd_fds(struct arglist *ifspec)
> +{
> +	int fd = -1;
> +	char *fdarg = NULL;
> +	struct vector_fds *result = NULL;
> +
> +	fdarg = uml_vector_fetch_arg(ifspec, "fd");
> +	fd = strtofd(fdarg);
> +	if (fd == -1) {
> +		printk(UM_KERN_ERR "fd open: bad or missing fd argument");
> +		goto fd_cleanup;
> +	}
> +
> +	result = uml_kmalloc(sizeof(struct vector_fds), UM_GFP_KERNEL);
> +	if (result == NULL) {
> +		printk(UM_KERN_ERR "fd open: allocation failed");
> +		goto fd_cleanup;
> +	}
> +
> +	result->rx_fd = fd;
> +	result->tx_fd = fd;
> +	result->remote_addr_size = 0;
> +	result->remote_addr = NULL;
> +	return result;
> +
> +fd_cleanup:
> +	if (fd >= 0)
> +		os_close_file(fd);
> +	if (result != NULL)
> +		kfree(result);
> +	return NULL;
> +}
> +
>   static struct vector_fds *user_init_raw_fds(struct arglist *ifspec)
>   {
>   	int rxfd = -1, txfd = -1;
> @@ -578,6 +635,8 @@ struct vector_fds *uml_vector_user_open(
>   		return user_init_socket_fds(parsed, ID_L2TPV3);
>   	if (strncmp(transport, TRANS_BESS, TRANS_BESS_LEN) == 0)
>   		return user_init_unix_fds(parsed, ID_BESS);
> +	if (strncmp(transport, TRANS_FD, TRANS_FD_LEN) == 0)
> +		return user_init_fd_fds(parsed);
>   	return NULL;
>   }
>   
> 

We should also control enable/disable of recv/sendmmsg as an option here.

It can be made generic and be fed into get_transport_options() in 
vector_kern.c as an override.

-- 
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/